"Some of the most precious documents we possess about the Modern philosophers such as Descartes and Leibniz are the letters they wrote. To all and sundry. People who were asking them about their philosophy. Students they took on... And... I had this idea that if at some future date someone was going to collect my works, I wouldn't be embarrassed to see the letter, amongst those works..." Pathways to Philosophy: Seven Years On

Monday, September 9, 2013

Descartes' arguments for the existence of God

Thank you for your email of 19 October, with your essay for the University of London BA Modern Philosophy: Descartes, Locke, Berkeley, Hume module, in response to the question, 'Discuss the strengths and weaknesses of Descartes' arguments for the existence of God.'

Like you, I have just changed computers (my old beige G3 for a G5 which I bought on eBay) and am still at the stage where doing simple stuff seems harder rather than easier.

This is a very thorough investigation of Descartes' argument from the idea of Perfection and his version of the Ontological argument, with which I have no real disagreements.

It does seem rather odd to be asked to discuss the 'strengths' and 'weaknesses' of arguments which we know (or have assumed from the start) to be invalid. How can one invalid argument be 'stronger' or 'weaker' than another? Nevertheless, you do give credit where credit is due, pointing out the novelty of Descartes' argument from Perfection, as well as his novel take on Anselm's Ontological argument.

As there is little that I can find here to criticize, I will try to suggest some angles or ideas which you might not have considered, which, possibly, give Descartes' arguments more interest or bite for a modern reader.

Let's start with the argument from the idea of Perfection. What other examples can one think of involving the move from the alleged fact that I have an idea of X, to X's necessary existence? Consider the idea of infinity as such, which is implied by such claims as that the series of natural numbers is infinite, or the definition of an infinite set as one which maps onto a proper subset. On a realist or Platonist view of mathematical objects, the possibility of our forming the concept of the infinite is explained, admittedly in a non-causal way, in terms of the existence, e.g., of the infinite series of natural numbers. In Newtonian physics, space and time are infinite.

What gives the Platonist, or the Newtonian, the confidence to speak in such terms? Leave aside the claim that you'd have to believe in God to be a Platonist or Newtonian (true, in the case of Newton). There seems to be a fundamental clash here, with the very idea or principle of empiricism, which Kant attempted to resolve by talking of the infinite, or questions about infinite collections, being 'set as a task'. But aside from the fact that naive talk of infinity leads to some rather painful antinomies or contradictions (which is a less than conclusive case against the rationalist) it is difficult to see how the argument could be resolved to the satisfaction of both parties. The Platonist *sees*what is there to be seen. What is seen must exist because I see it, and my perception cannot be illusory.

Any attempt to determine the placing of onus of proof is bound to fail, because the Platonist won't accept the principle on which this is decided. To ask for 'proof' is to ask for an analysis consistent with the principles of empiricism. Why is the case any different if the idea in question is the idea of a Cartesian deity?

An argument works because it takes something you believe, and leads you by means of a series of indisputable steps to something you didn't previously believe (or at least know you believed). Descartes thinks he can do this with the idea of God because what he is claiming is that our very ability to judge 'degrees' of perfection implies (even if we didn't realize this) the idea of an absolute degree. This is analogous to saying, 'If you have the idea of a natural number, then you must have the idea of infinity.' To resist the conclusion, we are forced to give an alternative explanation, one which inevitably involves saying more, giving more information (as e.g. in mathematical intuitionism or formalism).

Or consider the question of 'other minds' much discussed by analytic philosophers. A case could be made that any attempt to give an epistemological account, in terms of perception of the language or behaviour of other persons inevitably leads to a view which is unable to distinguish the belief in other minds from belief in the existence of 'zombies' (as in David Chalmers' thought experiment) which behave in every way as if they had minds. If you didn't have the concept of 'another mind' to start with, you could never acquire it. Therefore other minds exist.

I don't have much to say about the ontological argument. As you state, Descartes leaves us with the alternative, 'If God exists his existence is necessary' or 'If God doesn't exist his existence is impossible.' In other words, Descartes' claim, based on clear and distinct perception, is that God's existence is not impossible. That's all he has to prove!

How does one decide the onus of proof? Isn't this like the previous case? Can't we say that here too, the objector has more work to do, is obliged to give an alternative, informative account of what Descartes 'thinks' he is thinking about when he thinks about God? 'There is no contradiction in the idea of a necessarily existing being: prove me wrong.'